1. Field of the Invention
The present invention relates to a leak-check apparatus of a fuel-vapor-processing system, a fuel-temperature estimation apparatus and a fuel-temperature-sensor diagnosis apparatus.
2. Description of Related Art
U.S. Pat. No. 6,082,337 (JP-A-11-101162) discloses an apparatus, which is used for checking a leak on a passage of a fuel-vapor-processing system during a running state of the engine. In a running state of the engine, however, the level of fuel in a fuel tank varies. It is thus difficult to check a leak with a high degree of precision during a running state of the engine.
On the other hand, JP-A-6-81727 (Japan Patent No. 2,745,991) discloses leak-check processing, which is carried out after the engine is stopped. However, leak-check processing, which is carried out after the engine is stopped, exhausts the battery.
U.S. Pat. No. 5,263,462 discloses an apparatus, which is used for detecting a pressure in the passage when the temperature of the fuel tank increases by a predetermined quantity, and used for checking a leak of the same system on the basis of this pressure. When the ambient temperature is low, however, the temperature of fuel in the fuel tank may not increase. Thus, the number of times the leak-check processing is carried out decreases.
In the leak-check processing, a leak is checked by hermetically sealing the passage of the system. Thus, when the passage of the system is opened after the leak-check processing, a flow is generated in the system due to a difference in pressure between the system and the atmosphere. If a flow is generated in a canister, for example, fuel vapor transits to an undesirable state in some cases.
In leak-check processing, detection of a small leak is also demanded. In the case of a small leak, however, it takes a long time to generate a detectable change in pressure. Thus, in order to detect a small leak, a long check time is required. During such a long check time, however, it is quite within the bounds of possibility that the operating condition of the engine changes. It is thus difficult to detect a small leak.
JP-A-6-81727 discloses a leak-check apparatus provided with a sensor for detecting a temperature of fuel in the fuel tank. This apparatus finds a difference in fuel temperature between a stopped state of the engine and a start of the engine. If the difference in fuel temperature is found greater than a predetermined value, a leak is checked on the basis of an internal pressure of the fuel tank. However, the fuel-temperature sensor increases the number of components and brings about an increase in assembly man-hour.